Thermosetting resin compositions containing maleimide and/or vinyl compounds

ABSTRACT

In accordance with the present invention, there are provided novel thermosetting resin compositions which do not require solvent to provide a system having suitable viscosity for convenient handling. Invention compositions have the benefit of undergoing rapid cure. The resulting thermosets are stable to elevated temperatures, are highly flexible, have low moisture uptake and are consequently useful in a variety of applictions, e.g., in adhesive applications since they display good adhesion to both the substrate and the device attached thereto.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/580,026, filed May 26, 2000, which is a continuation-in-part of U.S.patent application Ser. No. 09/107,897, filed Jun. 29, 1998, now U.S.Pat. No. 6,187,886, which itself is a continuation-in-part of U.S.patent application Ser. No. 08/711,982, filed Sep. 10, 1996 (now U.S.Pat. No. 5,789,757); this application also claims the benefit of anearlier effective filing date from U.S. patent application Ser. No.08/460,495, filed Jun. 2, 1995 (now U.S. Pat. No. 6,034,195), which is acontinuation-in-part of U.S. patent application Ser. No. 08/300,721,filed Sep. 2, 1994 (now U.S. Pat. No. 6,034,194), the disclosures ofeach of which are hereby expressly incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to thermosetting resin compositions anduses therefor. In a particular aspect, the present invention relates tothermosetting resin compositions containing maleimide resins, vinylresins, or both.

BACKGROUND OF THE INVENTION

Bismaleimides per se occupy a prominent position in the spectrum ofthermosetting resins. Indeed, several bismaleimides are commerciallyavailable. Bismaleimide resins are used as starting materials for thepreparation of thermoset polymers possessing a wide range of highlydesirable physical properties. Depending on the particular resin andformulation, the resins provide cured products having excellent storagestability, heat resistance, as well as good adhesive, electrical andmechanical properties. Accordingly, bismaleimide resins have been usedfor the production of moldings, heat-resistant composite materials, hightemperature coatings and for the production of adhesive joints.Typically, however, in any particular resin formulation there is atrade-off between the various properties. For example, in theformulation of “snap” cure adhesives (i.e., adhesives that cure in twominutes or less at ≦200° C.), it is desirable to use a system which doesnot require the addition of diluent to facilitate handing. In otherwords, snap cure products require formulations containing 100% reactivematerials. Thus, it is desirable to prepare snap cure resins which areliquid at or about room temperature (i.e., low viscosity materials) forease of handling.

Unfortunately, up until now, it has not proved possible to formulatebismaleimide compositions that are both quick curing, easy to handle(i.e., liquid at or about room temperature), and have low moistureuptake. Consequently, it is a desideratum to provide thermosettingbismaleimide resin compositions that produce cured resins exhibiting acombination of highly desirable physical properties, including acombination of rapid curing and low water absorption.

A particular disadvantage of the use of bismaleimide resins for thetypes of applications described above is that, at room temperature, suchmaterials exist as solid resins which require the addition of liquiddiluents, in order for such resins to achieve a useful and processableviscosity. This difficulty has been compounded by the poor solubility ofbismaleimides in organic solvents. This poor solubility generallynecessitates the use of polar diluents, such as N-methyl-2-pyrrolidoneor dimethylformamide. These diluents are undesirable, inter alia, fromthe viewpoint of environmental pollution. Therefore, it is anotherdesideratum to provide bismaleimide resins that require little, if any,non-reactive diluent to facilitate handling.

One approach to solving the problem of a need for a diluent has been touse reactive liquid diluents. For example, the co-cure of simplebismaleimides with relatively simple divinyl ethers is known in the art.The use of such diluents is advantageous in that these materials becomeincorporated into the thermosetting resin composition, and hence do notcreate disposal problems. However, the range of suitable liquid reactivediluents is very limited. Many of the available diluents are restrictedby the low boiling points thereof, and, therefore, the high volatilitythereof; by the odor of such materials; by the toxicity of suchmaterials and/or problems with skin irritation induced thereby; by thepoor ability of such materials to solubilize bismaleimides; by the highviscosity of such materials, which, again, limits the bismaleimidesolubility and also leads to little or no tack in the formulation; bythe poor thermal stability and/or hydrolytic stability of suchmaterials; by the incompatibility of such materials with otherformulation modifiers, and the like. In particular, since the diluentsbecome an integral component of the thermosetting resin composition,they necessarily influence its properties. Consequently, it is anotherdesideratum to provide combinations of bismaleimide resins with reactivediluents which do not suffer from the above-described drawbacks and thatproduce cured resins exhibiting a combination of highly desirablephysical properties, including rapid curing and low water absorption.

Accordingly, there has existed a definite need for bismaleimide resinsthat produce cured resins exhibiting a combination of highly desirablephysical properties, including rapid curing and low water absorption.There has existed a further need for bismaleimide resins that requirethe additions of little, if any, non-reactive diluent to facilitatehandling. And there has existed a still further need for combinations ofbismaleimide resins with reactive diluents which do not suffer from thelimitations of known reactive resins and that produce cured resinsexhibiting a combination of highly desirable physical properties,including rapid curing and low water absorption. The present inventionsatisfies these and other needs and provides further related advantages.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with the present invention, we have developed novelthermosetting resin compositions which meet all of the above-describedneeds, i.e., produce cured resins exhibiting a combination of highlydesirable physical properties, including rapid curing and low waterabsorption, and which require little, if any, diluent to provide asystem of suitable viscosity for convenient handling. In another aspectof the invention, we have developed novel combinations of bismaleimideresins with reactive diluents, which do not suffer from the limitationsof known reactive resins and that produce cured resins exhibiting acombination of highly desirable physical properties, including rapidcuring and low water absorption. The resulting cured resins are stableat elevated temperatures, are highly flexible, have low moisture uptakeand good adhesion.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, there are provided novelmaleimide resins of general formula I, as follows:

wherein:

-   -   m=1, 2 or 3,    -   each R is independently selected from hydrogen or lower alkyl,        and    -   X is a monovalent or polyvalent radical selected from:        -   high molecular weight branched chain alkyl, alkylene or            alkylene oxide species having from about 12 to about 500            atoms in the backbone thereof,        -   aromatic groups having the structure:        -    wherein:        -   n=1, 2 or 3,        -   each Ar is a monosubstituted, disubstituted or            trisubstituted aromatic or heteroaromatic ring having in the            range of 3 up to 10 carbon atoms, and        -   Z is a high molecular weight branched chain alkyl, alkylene            or alkylene oxide species having from about 12 to about 500            atoms in the backbone thereof,        -   as well as mixtures thereof.

It is a distinct advantage of the bismaleimide resins of Formula I thatthey can be used with little, if any, added diluent. Generally, for easyhandling and processing, the viscosity of a thermosetting resincomposition must fall in the range of about 10 to about 12,000centipoise, preferably from about 10 to about 2,000 centipoise.Maleimide resins of Formula I typically require no added diluent, orwhen diluent is used with resins contemplated by Formula I, far lessdiluent is required to facilitate handling than must be added toconventional maleimide-containing thermosetting resin systems. Preferredmaleimide resins of Formula I include stearyl maleimide, oleyl maleimideand behenyl maleimide, 1,20-bismaleimido-10,11-dioctyl-eicosane (whichlikely exists in admixture with other isomeric species produced in theene reactions employed to produce dimer acids from which thebismaleimide is prepared, as discussed in greater detail below), and thelike, as well as mixtures of any two or more thereof.

When a diluent is added, it can be any diluent which is inert to thebismaleimide resin and in which the resin has sufficient solubility tofacilitate handling. Representative inert diluents includedimethylformamide, dimethylacetamide, N-methylpyrrolidone, toluene,xylene, methylene chloride, tetrahydrofuran, methyl ethyl ketone,monoalkyl or dialkyl ethers of ethylene glycol, polyethylene glycol,propylene glycol or polypropylene glycol, glycol ethers, and the like.

Alternatively, the diluent can be any reactive diluent which, incombination with bismaleimide resin, forms a thermosetting resincomposition. Such reactive diluents include acrylates and methacrylatesof monofunctional and polyfunctional alcohols, vinyl compounds asdescribed in greater detail herein, styrenic monomers (i.e., ethersderived from the reaction of vinyl benzyl chlorides with mono-, di-, ortrifunctional hydroxy compounds), and the like.

Now in accordance with the invention there has been found an especiallypreferred class of reactive diluents corresponding to vinyl or polyvinylcompounds having the general formula:Y—[Q_(0,1)—CR═CHR]_(q)  (II)wherein:

-   -   q is 1, 2 or 3,    -   each R is independently as defined above,    -   each Q is independently selected from —O—, —O—C(O)—, —C(O)— or        —C(O)—O—, and    -   Y is selected from:        -   saturated straight chain alkyl, alkylene or alkylene oxide,            or branched chain alkyl, alkylene or alkylene oxide,            optionally containing saturated cyclic moieties as            substituents on said alkyl, alkylene or alkylene oxide chain            or as part of the backbone of the alkyl, alkylene or            alkylene oxide chain, wherein said alkyl, alkylene or            alkylene oxide species have at least 6 carbon atoms,            preferably wherein said alkyl, alkylene or alkylene oxide            species are high molecular weight branched chain species            having from about 12 to about 500 carbon atoms,        -   aromatic moieties having the structure:        -    wherein each R is independently as defined above, Ar is as            defined above, t falls in the range of 2 up to 10 and u is            1, 2 or 3,        -   polysiloxanes having the structure:            —(CR₂)_(m′)—[Si(R′)₂—O]_(q′)—Si(R′)₂—(CR₂)_(n′)—        -    wherein each R is independently defined as above, and each            R′ is independently selected from hydrogen, lower alkyl or            aryl, m′ falls in the range of 1 up to 10, n′ falls in the            range of 1 up to 10, and q′ falls in the range of 1 up to            50,        -   polyalkylene oxides having the structure:            —[(CR₂)_(r)—O—]_(q′)—(CR₂)_(s)—        -    wherein each R is independently as defined above, r falls            in the range of 1 up to 10, s falls in the range of 1 up to            10, and q′ is as defined above,        -   as well as mixtures of any two or more thereof.

Exemplary vinyl or polyvinyl compounds embraced by the above genericstructure include stearyl vinyl ether, behenyl vinyl ether, eicosylvinyl ether, isoeicosyl vinyl ether, isotetracosyl vinyl ether,poly(tetrahydrofuran) divinyl ether, tetraethylene glycol divinyl ether,tris-2,4,6-(1-vinyloxybutane-4-)oxy-1,3,5-triazine,bis-1,3-(1-vinyloxybutane-4-)oxycarbonyl-benzene (alternately referredto as bis(4-vinyloxybutyl)isophthalate; available from Allied-SignalInc., Morristown, N.J., under the trade name Vectomer™ 4010), divinylethers prepared by transvinylation between lower vinyl ethers and highermolecular weight di-alcohols (e.g., α, ω-dihydroxy hydrocarbons preparedfrom dimer acids, as described above; an exemplary divinyl ether whichcan be prepared from such dimer alcohols is 10,11-dioctyleicosane-1,20-divinyl ether, which would likely exist in admixture withother isomeric species produced in ene reactions employed to producedimer acids), in the presence of a suitable palladium catalyst (see, forexample, Example 9), optionally hydrogenated α,ω-disubstitutedpolybutadienes, optionally hydrogenated α,ω-disubstituted polyisoprenes,optionally hydrogenated α,ω-disubstituted poly[(1-ethyl)-1,2-ethane],and the like. Preferred divinyl resins include stearyl vinyl ether,behenyl vinyl ether, eicosyl vinyl ether, isoeicosyl vinyl ether,poly(tetrahydrofuran) divinyl ether, divinyl ethers prepared bytransvinylation between lower vinyl ethers and higher molecular weightdi-alcohols (e.g., α,ω-dihydroxy hydrocarbons prepared from dimer acids,as described above; an exemplary divinyl ether which can be preparedfrom such dimer alcohols is 10,11-dioctyl eicosane-1,20-divinyl ether,which would likely exist in admixture with other isomeric speciesproduced in ene reactions employed to produce dimer acids), in thepresence of a suitable palladium catalyst (see, for example, Example 9),and the like.

Additionally, in accordance with another embodiment of the presentinvention, it has been found that divinyl compounds corresponding toFormula II where —Q— is —C(O)—O— and Y is a high molecular weightbranched chain alkylene species having from about 12 to about 500 carbonatoms are useful thermosetting resin compositions, even in the absenceof bismaleimide resins. When combined with suitable amounts of at leastone free radical initiator and at least one coupling agent, thesedivinyl ether resins, alone, are capable of forming thermosetting resincompositions exhibiting excellent physical properties, including rapidcure rates and low water absorption.

In accordance with yet another embodiment of the present invention,there are provided thermosetting resin compositions made of mixtures ofa vinyl compound of Formula II and a maleimide corresponding to thefollowing general formula (generally containing in the range of about0.01 up to about 10 equivalents of vinyl compound per equivalent ofmaleimide with in the range of about 0.01 up to about 1 eq. beingpreferred where the vinyl compound is a mono- or polyvinyl ether):

wherein:

-   -   m is as defined above,    -   each R is independently as defined above, and    -   X′ is a monovalent or polyvalent radical selected from:        -   saturated straight chain alkyl or alkylene, or branched            chain alkyl or alkylene, optionally containing saturated            cyclic moieties as substituents on said alkyl or alkylene            chain or as part of the backbone of the alkyl or alkylene            chain, wherein said alkyl or alkylene species have at least            6 carbon atoms, preferably wherein said alkyl or alkylene            species are high molecular weight branched chain species            having from about 12 to about 500 carbon atoms,        -   aromatic groups having the structure:        -    wherein        -   n is as defined above, Ar is as defined above, and Z′ is a            monovalent or polyvalent radical selected from:            -   saturated straight chain alkyl or alkylene, or branched                chain alkyl or alkylene, optionally containing saturated                cyclic moieties as substituents on said alkyl or                alkylene chain or as part of the backbone of the alkyl                or alkylene chain, wherein said species have at least 6                carbon atoms, preferably wherein said species are high                molecular weight branched chain species having from                about 12 to about 500 atoms as part of the backbone                thereof,            -   siloxanes having the structure:                —(CR₂)_(m′)—[Si(R′)₂—O]_(q)—Si(R′)₂—(CR₂)_(n′—)            -    wherein each R and R′ is independently defined as                above, and wherein each of m′, n′ and q is as defined                above,            -   polyalkylene oxides having the structure:                —[(CR₂)_(r)—O—]_(q′)—(CR₂)_(s)—            -    wherein each R is independently as defined above, and                wherein each of r, s and q′ is as defined above,        -   aromatic moieties having the structure:        -    wherein each R is independently as defined above, Ar is as            defined above, and each of t and u is as defined above,        -   siloxanes having the structure:            —(CR₂)_(m′)—[Si(R′)₂—O]_(q)—Si(R′)₂—(CR₂)_(n′)—        -    wherein each R and R′ is independently defined as above,            and wherein each of m′, n′ and q′ is as defined above,        -   polyalkylene oxides having the structure:            —[(CR₂)_(r)—O—]_(q′)—(CR₂)_(s)—        -    wherein each R is independently as defined above, and            wherein each of r, s and q′ is as defined above,        -   as well as mixtures of any two or more thereof.            Such mixtures possess a combination of highly desirable            physical properties, including both rapid cure rates and low            water absorption.

Exemplary bismaleimides embraced by Formula III include bismaleimidesprepared by reaction of maleic anhydride with dimer amides (i.e., α,ω-diamino hydrocarbons prepared from dimer acids, a mixture of mono-,di- and tri-functional oligomeric, aliphatic carboxylic acids; dimeracids are typically prepared by thermal reaction of unsaturated fattyacids, such as oleic acid, linoleic acid, and the like, which induces anene reaction, leading to the above-mentioned mixture of components). Anexemplary bismaleimide which can be prepared from such dimer amides is1,20-bismaleimido-10,11-dioctyl-eicosane, which would likely exist inadmixture with other isomeric species produced in the ene reactionsemployed to produce dimer acids. Other bismaleimides contemplated foruse in the practice of the present invention include bismaleimidesprepared from α,ω-aminopropyl-terminated polydimethyl siloxanes (such as“PS510” sold by Hüls America, Piscataway, N.J.), polyoxypropylene amines(such as “D-230”, “D-400”, “D-2000” and “T-403”, sold by Texaco ChemicalCompany, Houston, Tex.), polytetramethyleneoxide-di-p-aminobenzoates(such as the family of such products sold by Air Products, Allentown,Pa., under the trade name “Versalink” e.g., “Versalink P-650”), and thelike. Preferred maleimide resins of Formula III include stearylmaleimide, oleyl maleimide, behenyl maleimide,1,20-bismaleimido-10,11-dioctyl-eicosane (which likely exists inadmixture with other isomeric species produced in the ene reactionsemployed to produce dimer acids from which the bismaleimide is prepared,as discussed in greater detail elsewhere in this specification), and thelike, as well as mixtures of any two or more thereof.

In preferred embodiments of the present invention, when mixtures ofbismaleimides and divinyl compounds are employed, either X′ (of thebismaleimide) or Y (of the divinyl compound) can be aromatic, but bothX′ and Y are not both aromatic in the same formulation. Additionally, inpreferred embodiments of the present invention, when mixtures ofbismaleimides and divinyl compounds are employed, at least one of X′ orY is a high molecular weight branched chain alkylene species having fromabout 12 to about 500 carbon atoms.

Bismaleimides can be prepared employing techniques well known to thoseof skill in the art. The most straightforward preparation of maleimideentails formation of the maleamic acid via reaction of the correspondingprimary amine with maleic anhydride, followed by dehydrative closure ofthe maleamic acid with acetic anhydride. A major complication is thatsome or all of the closure is not to the maleimide, but to theisomaleimide. Essentially the isomaleimide is the dominant or evenexclusive kinetic product, whereas the desired maleimide is thethermodynamic product. Conversion of the isomaleimide to the maleimideis effectively the slow step and, particularly in the case of aliphaticamides, may require forcing conditions which can lower the yield.Nevertheless, in the case of a stable backbone such as that provided bya long, branched chain hydrocarbon (e.g.,—(CH₂)₉—CH(C₈H₁₇)—CH(C₈H₁₇)—(CH₂)₉—), the simple acetic anhydrideapproach appears to be the most cost effective method. Of course, avariety of other approaches can also be employed.

For example, dicyclohexylcarbodiimide (DCC) closes maleamic acids muchmore readily than does acetic anhydride. With DCC, the product isexclusively isomaleimide. However, in the presence of suitableisomerizing agents, such as 1-hydroxybenzotriazole (HOBt), the productis solely the maleimide. The function of the HOBt could be to allow theclosure to proceed via the HOBt ester of the maleamic acid (formed viathe agency of DCC) which presumably closes preferentially to themaleimide. However, it is unclear why such an ester should exhibit sucha preference. In any case, it is demonstrated herein that isomidegenerated by reaction of the bismaleamic acid of 10,11-dioctyleicosanewith either acetic acid anhydride or EEDQ(2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline) is isomerized to thebismaleimide by catalytic amounts of HOBt.3-Hydroxy-1,2,3-benzotriazine-4-one appears to be at least as effectiveas HOBt in effecting this isomerization, whereas N-hydroxysuccinimide issubstantially less so.

Likely, isomerizing agents such as HOBt add to the isoimide to yield theamic acid ester. If this exhibits any tendency whatsoever to close tothe imide, much less a strong bias for doing so, a route forinterconverting isoimide and imide is thereby established and thethermodynamic product, imide, should ultimately prevail. Thus if theinitial closure of ester formed in the DCC reaction yields any isoimide,or if any isoimide is produced by direct closure of the acid, thesituation will be subsequently “corrected” via conversion of theisoimide to the imide by the action of the active ester alcohol as anisomerizing agent.

One problem encountered with bismaleimides is a proclivity foroligomerization. This oligomerization is the principle impediment toyield in the synthesis of bismaleimides, and may present problems inuse. Radical inhibitors can mitigate this potential problem somewhatduring the synthesis but these may be problematic in use. Fortunately,oligomer may be removed by extracting the product into pentane, hexaneor petroleum ether, in which the oligomers are essentially insoluble.

Thermosetting resin compositions of the invention also contain in therange of 0.2 up to 3 wt % of at least one free radical initiator, basedon the total weight of organic materials in the composition, i.e., inthe absence of filler. As employed herein, the term “free radicalinitiator” refers to any chemical species which, upon exposure tosufficient energy (e.g., light, heat, or the like), decomposes into twoparts which are uncharged, but which each possesses at least oneunpaired electron. Preferred as free radical initiators for use in thepractice of the present invention are compounds which decompose (i.e.,have a half life in the range of about 10 hours) at temperatures in therange of about 70 up to 180° C.

Exemplary free radical initiators contemplated for use in the practiceof the present invention include peroxides (e.g., dicumyl peroxide,dibenzoyl peroxide, 2-butanone peroxide, tert-butyl perbenzoate,di-tert-butyl peroxide, 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane,bis(tert-butyl peroxyisopropyl)benzene, and tert-butyl hydroperoxide),azo compounds (e.g., 2,2′-azobis(2-methylpropanenitrile),2,2′-azobis(2-methylbutanenitrile), and1,1′-azobis(cyclohexanecarbonitrile)), and the like. Peroxide initiatorsare presently preferred because they entail no gas release upondecomposition into free radicals. Those of skill in the art recognize,however, that in certain adhesive applications, the release of gas (e.g.N₂) during cure of the adhesive would be of no real concern. Generallyin the range of about 0.2 up to 3 wt % of at least one free radicalinitiator (based on the total weight of the organic phase) will beemployed, with in the range of about 0.5 up to 1.5 wt % preferred.

Thermosetting resin compositions of the invention possess a variety ofphysical properties making them particularly adapted for use in thepreparation of “snap” cure adhesives. Such adhesives are useful, forexample, in die attach applications. When used in adhesive applications,it is desirable to add coupling agent(s) to the formulation.

As employed herein, the term “coupling agent” refers to chemical speciesthat are capable of bonding to a mineral surface and which also containpolymerizably reactive functional group(s) so as to enable interactionwith the adhesive composition. Coupling agents thus facilitate linkageof the adhesive composition to the substrate to which it is applied.

Exemplary coupling agents contemplated for use in the practice of thepresent invention include silicate esters, metal acrylate salts (e.g.,aluminum methacrylate), titanates (e.g., titaniummethacryloxyethylacetoacetate triisopropoxide), or compounds thatcontain a copolymerizable group and a chelating ligand (e.g., phosphine,mercaptan, acetoacetate, and the like). Generally in the range of about0.1 up to 10 wt % of at least one coupling agent (based on the totalweight of the organic phase) will be employed, with in the range ofabout 0.5 up to 2 wt % preferred.

Presently preferred coupling agents contain both a co-polymerizablefunction (e.g., vinyl moiety, acrylate moiety, methacrylate moiety,styrene moiety, cyclopentadiene moiety, and the like), as well as asilicate ester function. The silicate ester portion of the couplingagent is capable of condensing with metal hydroxides present on themineral surface of the substrate, while the co-polymerizable function iscapable of co-polymerizing with the other reactive components ofinvention adhesive composition. Especially preferred coupling agentscontemplated for use in the practice of the invention are oligomericsilicate coupling agents such as poly(methoxyvinylsiloxane).

In addition to the incorporation of coupling agents into inventionadhesive compositions, it has also been found that the optionalincorporation of a few per cent of the precursor bismaleamic acidgreatly increases adhesion. Indeed, good adhesion is retained even afterstrenuous exposure to water.

Adhesive compositions of the invention possess a combination of physicalproperties believed to be critical to successful commercial application:

-   -   1. The adhesive compositions have good handling properties,        needing little, if any, inert diluent added thereto (i.e., the        resin compositions form 100% reactive systems of sufficiently        low viscosity);    -   2. The adhesive compositions are capable of rapid (“snap”) cure,        i.e., curing in two minutes or less (preferably as short as 15        seconds) at ≦200° C.;    -   3. The resulting thermosets are stable to at least 250° C.,        wherein “stable” is defined as less than 1% weight loss at        250° C. when subjected to a temperature ramp of 10° C./min. in        air via thermogravimetric analysis (TGA);    -   4. The resulting thermosets are sufficiently flexible (e.g.,        radius of curvature >1.0 meter for a 300 mil² silicone die on a        copper lead frame using a cured bond line ≦2 mils) to allow use        in a variety of high stress applications;    -   5. The resulting thermosets exhibit low-moisture uptake (in        nonhermetic packages); and    -   6. The resulting thermosets exhibit good adhesion to substrates,        even after strenuous exposure to moisture.

Adhesive compositions of the invention can be employed in thepreparation of die-attach pastes comprising in the range of about 10 upto 80 wt % of the above-described thermosetting resin composition, andin the range of about 20 up to 90 wt % filler. Fillers contemplated foruse in the practice of the present invention can be electricallyconductive and/or thermally conductive, and/or fillers which actprimarily to modify the rheology of the resulting composition. Examplesof suitable electrically conductive fillers which can be employed in thepractice of the present invention include silver, nickel, copper,aluminum, palladium, gold, graphite, metal-coated graphite (e.g.,nickel-coated graphite, silver-coated graphite, and the like), and thelike. Examples of suitable thermally conductive fillers which can beemployed in the practice of the present invention include graphite,aluminum nitride, silicon carbide, boron nitride, diamond dust, alumina,and the like. Compounds which act primarily to modify rheology includefumed silica, alumina, titania, high surface area smectite clays, andthe like.

In accordance with yet another embodiment of the present invention,there are provided assemblies of components adhered together employingthe above-described adhesive compositions and/or die attachcompositions. Thus, for example, assemblies comprising a first articlepermanently adhered to a second article by a cured aliquot of theabove-described adhesive composition are provided. Articles contemplatedfor assembly employing invention compositions include memory devices,ASIC devices, microprocessors, flash memory devices, and the like.

Also contemplated are assemblies comprising a microelectronic devicepermanently adhered to a substrate by a cured aliquot of theabove-described die attach paste. Microelectronic devices contemplatedfor use with invention die attach pastes include copper lead frames,Alloy 42 lead frames, silicon dice, gallium arsenide dice, germaniumdice, and the like.

In accordance with still another embodiment of the present invention,there are provided methods for adhesively attaching two component partsto produce the above-described assemblies. Thus, for example, a firstarticle can be adhesively attached to a second article, employing amethod comprising:

-   -   (a) applying the above-described adhesive composition to said        first article,    -   (b) bringing said first and second article into intimate contact        to form an assembly wherein said first article and said second        article are separated only by the adhesive composition applied        in step (a), and thereafter,    -   (c) subjecting said assembly to conditions suitable to cure said        adhesive composition.

Similarly, a microelectronic device can be adhesively attached to asubstrate, employing a method comprising:

-   -   (a) applying the above-described die attach paste to said        substrate and/or said microelectronic device,    -   (b) bringing said substrate and said device into intimate        contact to form an assembly wherein said substrate and said        device are separated only by the die attach composition applied        in step (a), and thereafter,    -   (c) subjecting said assembly to conditions suitable to cure said        die attach composition.

Conditions suitable to cure invention die attach compositions comprisesubjecting the above-described assembly to a temperature of less thanabout 200° C. for about 0.25 up to 2 minutes. This rapid, short durationheating can be accomplished in a variety of ways, e.g., with an in-lineheated rail, a belt furnace, or the like.

In accordance with a still further embodiment of the present invention,there is provided a method for the preparation of bismaleimides fromdiamines. The invention synthetic method comprises:

-   -   adding diamine to a solution of maleic anhydride,    -   adding acetic anhydride to said solution once diamine addition        is complete, and then allowing the resulting mixture to stir        overnight, and thereafter    -   treating the resulting reaction mixture with a suitable        isomerizing agent.

Diamines contemplated for use in the practice of the present inventioninclude saturated and unsaturated dimer diamines (such as the dimeramines sold by Henkel Corporation, Ambler, Pa., under the trade name“Versamine 552” and “Versamine 551”), α,ω-aminopropyl-terminatedpolydimethyl siloxanes (such as “PS510” sold by Hüls America,Piscataway, N.J.), polyoxypropylene amines (such as “D-230”, “D-400”,“D-2000” and “T-403”, sold by Texaco Chemical Company, Houston, Tex.),polytetramethyleneoxide-di-p-aminobenzoate (such as the family of suchproducts sold by Air Products, Allentown, Pa., under the trade name“Versalink” e.g., “Versalink P-650”), and the like. Diamine and maleicanhydride are typically combined in approximately equimolar amounts,with a slight excess of maleic anhydride preferred. Isomerizing agentscontemplated for use in the practice of the present invention include1-hydroxybenzotriazole, 3-hydroxy-1,2,3-benzotriazine-4-one,1-hydroxy-7-azabenzotriazole, N-hydroxysuccinimide, and the like.

The invention will now be described in greater detail by reference tothe following non-limiting examples.

EXAMPLE 1

Preparation of the bismaleimide of hydrogenated dimer acid diamine(Henkel Corp. Versamine 552) by closure of the bismaleamic acid withacetic anhydride to a mixture of isomaleimide and maleimide, followed byisomerization of the isomaleimide to maleimide with1-hydroxybenzotriazole (HOBt) under mild conditions. A solution of 30.0g of Versamine 552 in 90 mL of anhydrous tetrahydrofuran (THF) wasslowly added to a solution of 12.5 g of maleic anhydride in 60 mL ofTHF. One hour after completion of the addition, 125 mL of aceticanhydride was added and the reaction mixture stirred overnight underargon atmosphere.

A Fourier transform infrared attenuated total reflectance (FTIR ATR)spectrum indicated substantial conversion of the amic acid to theisoimide, with little if any amide. The reaction mixture was brought toreflux and maintained there for three hours. FTIR now indicated amixture of isoimide and maleimide with the former apparently(uncalibrated spectrum) predominating. Benzoquinone, 0.1 g, was added tothe reaction mixture and the solvent/acetic anhydride/acetic acidstripped under vacuum (ultimately 0.1 mm Hg) at 30° C. The resultingresidue was taken up in 75 mL of fresh THF and 10.2 g of HOBt (<5% H₂Omaterial) was added and dissolved in at room temperature.

An FTIR spectrum one hour after the addition indicated that theisomaleimide in the mixture had been largely, perhaps completely,consumed. Most of it appeared to have been converted to maleamic acidHOBt ester. The reaction mixture was stirred overnight. FTIR thenindicated essentially complete conversion to the maleimide.

The solvent was stripped off at 30° C. and the residue extracted 2× withseveral hundred mL of pentane. The combined pentane fractions werechilled in a Dry Ice/isopropyl alcohol bath, which caused a white solidto crystallize out. (The solid is thought to be the acetate of HOBt,with some free HOBt). The pentane suspension was filtered cold, allowedto warm to room temperature, dried over anhydrous MgSO₄ and the solventstripped to give 16.9 g (43.8%) of high purity product (as determined byFTIR).

EXAMPLE 2

Bismaleamic acid was generated from 10.0 g of Versamine 552 and 3.9 g ofmaleic anhydride, each in 40 mL of THF.2-Ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ), 9.3 g, was added.Monitoring by FTIR indicated that two days sufficed to effectessentially complete conversion to isomaleimide. HOBt, 4.9 g, wasdissolved in the reaction mixture. Monitoring by FTIR indicated that sixhours sufficed to convert all the isoimide to imide. The solvent wasstripped off and the residue extracted with pentane to yield 6.0 g ofproduct bismaleimide, contaminated with quinoline from the EEDQ.

EXAMPLE 3

E. C. Martin and A. A. DeFusco, in U.S. Statutory Invention RegistrationNo. H424 (Feb. 2, 1988) teach the preparation of bismaleimide from“dimer diamine” (source not given but material NOT having had theolefinic unsaturation removed) by means of HOBt and DCC. However, themaximum yield of bismaleimide reported is 50%. Thus, following theprocedure of Martin and Fusco, the bismaleimide of Versamine 552 (HenkelCorp.) was prepared using dicyclohexylcarbodiimide (DCC) and1-hydroxybenzotriazole (HOBt). A solution of 50.0 g (0.179 amine equiv)of Versamine 552 in 60 mL of anhydrous tetrahydrofuran (THF) was addedslowly under argon atmosphere to a solution of 20.2 g (0.206 mole) ofmaleic anhydride in 300 mL of THF. The reaction mixture was stirred foran hour after completion of the addition and then 25.2 g (0.186 mole) ofHOBt (<5% H₂O) was dissolved in. The stirred reaction mixture waschilled in an ice bath and melted DCC added neat in portions to a totalof 49.2 g (0.238 mole). After completion of this addition, the reactionmixture was stirred in the ice bath for another hour. The ice bath wasthen removed and the stirred reaction mixture allowed to warm to roomtemperature overnight. The reaction mixture was filtered and theresulting solid was washed with THF. All THF phases were combined, 0.2 gmethoxyphenol was added and the THF stripped on a rotary evaporator at30° C. A thick, semisolid residue resulted. This residue was extractedwith hexane and the hexane stripped to give 40.7 g (63.3%) of a productwhich still had some solid impurity. This material was extracted withpentane, which cleanly separated the solid impurity. The pentane extractwas dried over MgSO₄ and the solvent stripped to give 32.1 g (49.9%) oflightly colored, low viscosity material with the expected FTIR spectrum.

EXAMPLE 3A

The monomaleimide of oleylamine was prepared using a method similar tothe one described in Example 3. Oleylamine was obtained from AldrichChemical Company (Milwaukee, Wis.). The amine (40.0 grams, 150 meqs) wasdissolved in 100 ml of anhydrous THF. This solution was slowly added(under an argon purge) to a mechanically stirred solution containingmaleic anhydride (14.7 g, 150 meqs) dissolved in 100 ml of anhydrousTHF. Stirring was continued for another hour after the addition wascomplete. The stirred reaction mixture was then cooled via an externalice bath and 30.8 g (149 meqs) dicyclohexylcarbodiimide (DCC), dissolvedin 30 mls anhydrous THF, was added. The chilled mixture was stirred foran additional hour before 19.7 g (146 meqs) of 1-hydroxybenzotriazole(HOBt) was added. The mixture was allowed to warm up to room temperaturewhile stirring was continued for another sixteen hours. The reactionmixture was filtered and the filtered residue was washed with additionalTHF. The combined THF solutions were stripped on a rotary evaporator at40° C. until the pressure under full mechanical vacuum was ≦0.5 torr.The viscous residue was then dissolved in pentane. The pentane solutionwas extracted five times with 50 ml portions of aqueous methanol (70%MeOH). Magnesium sulfate was added to the washed pentane solutionfraction and it was allowed to settle overnight in a refrigerator. Thesolution was warmed the next morning to room temperature, filtered, andthe solvent stripped off in a rotary evaporator (using water aspirator,followed by full mechanical vacuum until the pressure remained ≦0.5 torrfor one hour). The product recovered was a light brown, low viscosityliquid with an FTIR spectrum consistent with what one would predict forthe expected structure.

EXAMPLE 3B

A diacrylate was prepared as follows from the dimer diol derived fromoleic acid. This diol was obtained from Unichema North America (Chicago,Ill.) under the designation Pripol 2033. Approximately 53.8 grams ofPripol 2033 and 22.3 grams of triethylamine (reagent grade from AldrichChemical Co., Milwaukee, Wis.) were dissolved in 136.0 grams of dryacetone. This solution was chilled to 5° C. in an ice bath while thecontents of the flask were blanketed under a slow argon purge. Thesolution was subjected to mechanical stirring while acroyl chloride(18.1 grams dissolved in 107.3 grams of dry acetone) was added dropwiseover a two hour period. Stirring was continued for another hour and thebath was allowed to warm up to room temperature. Approximately 7.1 mg ofmethoxy hydroquinone (inhibitor) was added to the final reaction productand the acetone was removed on a rotary evaporator. The product was thendissolved in methylene chloride and this solution was then extractedthree times with 7% aqueous sodium bicarbonate and another two timeswith 18 meg-ohm water. The solution was dried over magnesium sulfate andthen filtered. Finally, the methylene chloride solvent was removed underfull mechanical vacuum on the rotary evaporator. An FTIR analysis ofthis product showed a characteristic ester absorption around 1727 wavenumbers. The final yield was 71% (based on the starting Pripol 2033).

EXAMPLE 4

This example illustrates improvement in yield obtained by using3-hydroxy-1,2,3-benzotriazin-4-one (HOBtCO) instead of HOBt. Thebismaleamic acid of Versamine 552 was prepared by the dropwise additionover an hour (dry argon atmosphere) of a solution of 144.0 g ofVersamine 552 in 100 mL of dry dichloromethane (CH₂Cl₂) to a stirredsolution of 50.4 g maleic anhydride in 300 mL of dry CH₂Cl₂ chilled inan ice bath. The ice bath was removed at the end of the addition and thereaction mixture stirred for another hour. The ice bath was then putback in place and 84.0 g (100%) of 3-hydroxy-1,2,3-benzotriazin-4-onewas added. To the chilled reaction mixture was then added a solution of106.1 g of DCC in 100 mL of CH₂Cl₂ over 30 minutes, with stirring. Aftercompletion of the addition, the ice bath was removed and the reactionmixture stirred overnight at room temperature. The reaction mixture wassuction-filtered and the collected solid was washed twice with 100 mLportions of CH₂Cl₂, which were combined with the original CH₂Cl₂filtrate. The CH₂Cl₂ was stripped on a rotary evaporator, at 35-40° C.,ultimately under oil-pump vacuum (0.1 Torr). The resulting residue wasextracted twice with 500 mL portions of pentane and once with a 1000 mLportion of pentane, all of which were combined and stripped on therotary evaporator. The original residue was extracted with more pentanefor a final total of four liters of pentane. After condensation to avolume of 500 mL, the solution was stored in the freezer overnight. Itwas allowed to warm to room temperature, suction-filtered through finefilter paper and the remaining pentane stripped to yield 145.0 g (80.0%)of the bismaleimide.

EXAMPLE 5

This example demonstrates that a very satisfactory yield may be obtainedusing much less than an equivalent of the coreactant compound,3-hydroxy-1,2,3-benzotriazin-4-one (HOBtCO), and that it may be addedafter the DCC. The bismaleamic acid of Versamine 552 was generated as inExample 4 from 136.5 g of Versamine 552 and 46.3 g of maleic anhydride,except that the solvent was THF rather than CH₂Cl₂. To the chilled (icebath) reaction mixture was added a THF solution of DCC containing 100.5g of DCC. After an FTIR spectrum showed that the amic acid had beenentirely converted to isoimide, 12 g (15%) of HOBtCO was added and thereaction mixture maintained at 45° C. for four hours, which sufficed, byFTIR, to convert the isoimide entirely to imide. Workup as in thepreceding example resulted in a yield of 122 g (70%) of thebismaleimide.

EXAMPLE 6

This example illustrates the use of 1-hydroxy-7-aza-1,2-3-benzotriazole(HOAt) as the coreactant compound, again at a low level. Using theprocedure described in the preceding example but with 20% HOAt, 51.5 gof Versamine 552 yielded 48.8 g (70.0%) of the BMI. Separation of theHOAt from the reaction product was facile and 4.4 g was recovered.

EXAMPLE 7

The following experiments demonstrate improvements in the yield,obtained by the procedure of Martin and Fusco by changes in procedureand protocol while still using HOBt. The procedure and protocol used isthat detailed in Example 4 in which 3-hydroxy-1,2,3-benzotriazin-4-oneis used except that the reaction solvent was THF in all cases hererather than the dichloromethane used in Example 4. A reaction using 100%HOBt gave a yield of 51.9%; four reactions using 80% HOBt gave yields of56.8, 60.0, 65.1 and 70,2%, respectively. Also, a reaction employingdimer diamine in which the olefinic unsaturation has not been removed,as in U.S. Statutory Invention Registration No. H424 (Henkel Versamine551 rather than 552), and 80% HOBt gave a yield of 52.2% of thecorresponding BMI.

Examples 4-7 show that by variations in solvent and procedures, yieldsas high as 70% may be obtained using HOBt and as high as 80% using3-hydroxy-1,2,3-benzotriazin-4-one (HOBtCO) in lieu of HOBt. Also therealization in the course of the present work that compounds such asHOBt and HOBtCO are potent agents for the isoimide to imideisomerization means that the reaction may be run with less than a fullequivalent of such. The fact that such compounds are first consumed andthen liberated during the cyclodehydration, and are thus in principlecatalysts, does not of itself necessarily imply that they may be used atless than a full equivalent since the potentially competing reaction ofdirect cyclodehydration of the amic acid by DCC to the isoimide wouldstill be of concern. However, as it turns out, HOBt, HOBtCO, and thelike are effective at promoting the facile isomerization which leads tothe desired product.

EXAMPLE 8

A masterbatch of the bisisomaleimide of Versamine 552 was prepared from30.0 g of the amine, dissolved in 80 mL of anhydrous THF and addeddropwise to a solution of 11.7 g of maleic anhydride in 100 mL ofanhydrous THF to yield the bismaleamic acid, followed by the addition of125 mL of neat acetic anhydride. One half of this reaction mixture wasallowed to stand for three days at room temperature. The solvent andexcess acetic anhydride were stripped to leave the isomaleimide.Portions of this isomaleimide were treated as follows. A 5.0 g samplewas dissolved in anhydrous THF along with 2.6 g of3-hydroxy-1,2,3-benzotriazin-4-one (HOBtCO). This solution was allowedto stand overnight, which sufficed to effect complete conversion to themaleimide, ultimately recovered in 56% yield. Another 5.0 g of theisomaleimide was treated with 2.3 g of HOBt in the same manner; a 46%yield of bismaleimide was recovered as well as a larger amount ofoligomerized material than in the HBtCO reaction. A third portion of theisomaleimide, 4.9 g, was treated with 2.1 g of N-hydroxysuccinimide inacetonitrile solution. In this case, overnight reflux was used to effectconversion to the maleimide, recovered in only 36% yield.

EXAMPLE 9

A divinyl ether was prepared as follows from the dimer diol derived fromoleic acid employing Pripol 2033 dimer diol obtained from Unichema NorthAmerica (Chicago, Ill.), vinyl propyl ether obtained from BASF Corp.(Parsippany, N.J.), and palladium 1,10-phenanthroline diacetate[Pd(phen)(OAc)₂]. Thus, the Pripol was pre-dried over molecular sieves(3A) approximately 3 hours prior to use. Next, to a clean and dry 1liter flask, with large oval Teflon stir bar, was added 149.1 grams(523.3 meqs) of Pripol 2033, 280 grams (3256 meqs) of vinyl propylether, and 1.0 grams Pd(phen) (AcO)₂ (2.5 meqs). The head space of theflask was purged with argon and the reaction flask fitted with an oilbubbler (to eliminate any pressure build up in the flask). The flask wasplaced on a magnetic stir plate and stirring initiated and continued forapproximately 48 hours. The solution color changed from a light yellowto a deep dark brown. After 48 hours, an aliquot was removed and thebulk of the vinyl propyl ether was blown off using argon. An FTIRanalysis was performed on the residue and it was determined thatvirtually all the alcohol had reacted (i.e., no OH absorbance between3400 and 3500 cm⁻¹ remained).

To the original solution approximately 10-15 grams of activated charcoalwas added. The solution was mixed for approximately 1 hour on themagnetic stir plate, then about 5 grams of Celite was added. Theactivated charcoal and Celite were removed via suction filtrationthrough a fritted funnel packed with additional Celite (about anadditional 15 grams). The solution that passed through the funnelretained a slight brown color.

The bulk of the excess vinyl propyl ether was then removed using arotary evaporator at a bath temperature of 35-40° C. under a partial(water aspirator) vacuum. Once condensation stopped, the cold traps wereemptied and replaced. A full mechanical vacuum was then applied andcontinued at the 35-40° C. bath temperature for approximately 1 hour.The vacuum decreased to under 1.0 torr within an hour. Product recoveredat this point was a light brown, low viscosity liquid.

The last traces of propyl vinyl ether were removed using a falling filmmolecular still (operated at a strip temperature of 70° C. and a vacuumof less than one torr). The product residence time in the still head wasabout 15 to 20 minutes and the complete stripping procedure requiredabout two hours. The product, following this strip, had no residual odorcharacteristic of the vinyl propyl ether. Thermogravimetric analysisshowed no significant weight loss by 200° C. The product, therefore, wasconsidered to be free of the vinyl ether starting material and anypropyl alcohol co-product.

EXAMPLE 9A

A divinyl ether was prepared from an alpha-omega terminated,hydrogenated 1,2-polybutadiene. This diol had a molecular weight ofapproximately 3,000 grams per mole and was obtained from Ken SeikaCorporation (Little Silver, N.J.) under the trade name GI-3000. Themethod used to synthesize the divinyl ether was analogous to the onedescribed in Example 9. Approximately 51.5 grams (34.4 meqs) of GI-3000was dissolved in 158.9 grams (1,840 meqs) of vinyl propyl ether. Themixture was stirred magnetically until a homogeneous solution wasobtained. Palladium 1,10-phenanthroline diacetate (0.53 grams, 1.33meqs) was then added and the entire mixture was allowed to stir for fivedays at room temperature under an argon atmosphere. An aliquot of thereaction product was removed and the volatiles (vinyl propyl ether andpropanol) were blown off. An FTIR trace obtained on this residuedemonstrated that the diol had been completely converted to thecorresponding divinyl ether.

The bulk of the reaction product was then worked up according to theprocedure described in the Example 9. The solution was decolorized usingactivated charcoal, treated with Celite, and the suspension was thenpassed through a filter packed with additional Celite. The bulk of theexcess vinyl propyl ether and propanol were removed using a rotaryevaporator (bath temperature ≦40° C.) at full mechanical pump vacuum.Evaporation was continued until the pressure fell to under one torr. Thelast traces of volatiles were stripped off using a falling filmmolecular still as described in Example 9. The final product was aviscous (although less so than the starting diol) straw colored liquid.

EXAMPLE 9B

Another oligomer diol was subjected to transvinylation. The alpha-omegadiol of hydrogenated polyisoprene was employed for this example, and isavailable from Ken Seika Corporation under the designation “TH-21”. Thisoligomer has an approximate molecular weight of 2,600 grams per mole.The same method as described in Example 9 was used to convert this diolto the corresponding divinyl ether. Thus, TH-21 (52.0 grams, 40 meqs)was dissolved in 83.7 grams of vinyl propyl ether (972 meqs) and 0.4grams (1.0 meq) of palladium 1,10-phenanthroline diacetate catalyst wasadded. The mixture was stirred magnetically at room temperature under anargon atmosphere for six days. An evaporated aliquot of the reactionmixture was found to be essentially free of alcohol functionalityaccording to FTIR analysis. The bulk of the reaction product was workedup as per the method described in Example 9. The final product was anamber, viscous liquid (again the viscosity of the divinyl compound wasconsiderably lower in viscosity than the starting diol).

EXAMPLE 9C

Iso-eicosyl alcohol, obtained from M. Michel and Co., Inc. (New York,N.Y.) was transvinylated according to the method described in Example 9.The alcohol (100.3 grams. 336 meqs) was dissolved in 377.4 grams of thevinyl propyl ester (4,383 meqs) and 1.0 gram (2.5 meqs) of palladium1,10-phenanthroline diacetate catalyst was added. The mixture wasmagnetically stirred under an argon atmosphere for four days. An FTIRtrace of the evaporated reaction product showed that no detectablealcohol residue remained. The product was worked up as previouslydescribed. The final material was a pale yellow liquid with a“water-like” viscosity.

EXAMPLE 9D

Behenyl alcohol (1-docosanol), obtained from M. Michel and Co., Inc.(New York, N.Y.) was transvinylated substantially as described inExample 9, however, since the starting alcohol was a waxy solid withlimited room temperature solubility in vinyl propyl ether, it wasnecessary to conduct the reaction at an elevated temperature. Thus, amixture of the alcohol (100.8 grams, 309 meqs), vinyl propyl ether(406.0 grams, 4,714 meqs), and palladium 1,10-phenanthroline diacetatecatalyst (1.0 gram, 2.5 meqs) was magnetically stirred at 50° C. underan argon atmosphere for 20 hours. Analysis of an evaporated aliquotafter this period showed that no detectable alcohol remained. Thebehenyl vinyl ether was worked up as described above. The final productwas an off-white waxy solid.

EXAMPLE 10

An organic adhesive vehicle was prepared using 2.78 grams (1.0equivalents) of the BMI prepared according to Example 8, 0.94 grams (0.5equivalents) of the divinyl ether prepared according to Example 9, and0.58 grams (0.5 equivalents) of Vectomer 4010 (i.e.,bis(4-vinyloxybutyl)isophthalate). An additional 1% by weight dicumylperoxide (initiator), 0.5% gamma-methacryloxypropyltrimethoxysilane(coupling agent), and 0.5%beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (coupling agent) wereadded to complete the organic adhesive mix.

Twenty-two percent by weight of the organic adhesive mixture was addedto 78% by weight of silver metal filler. The mixture was stirred underhigh shear until homogeneous. The resulting paste was then degassed at 1torr. The paste was dispensed onto silver plated copper lead framesusing a starfish dispense nozzle. Bare silicon dice (300×300 mils on aside) were then placed on top and compressed into the adhesive until a2.0 mil bondline had been attained (this process is virtuallyinstantaneous when using automated “pick and place” equipment. Theassembled parts were then cured on a heated surface (hot plate)controlled at 200° C. for two minutes. Additional void test parts (whichwere assembled in parallel using a 300×300 glass slide to replace thesilicon die) showed the cured adhesive film to be free of voiding. Halfof the assembled parts were subjected to tensile test immediately. Theother half were placed in a pressure cooker at 121° C. for 168 hours(i.e., one week). The pressure cooker is considered to be a veryaggressive test that has predictive value for the long term robustnessof adhesives used in non-hermetic environments.

Adhesion strength testing was performed on these parts using a “TiniusOlsen 10,000” tensile test machine. Steel cube studs (0.25×0.25×0.8inches) were attached at room temperature to the top of the die and thebottom of the lead frame using Loctite 415 cyanoacrylate glue. The cubeswere attached using a V-block fixturing device to assure theirco-linearity. Once the room temperature gluing operation was complete(˜one hour later), the entire assembly was loaded into the tensile testmachine. Pins were used to secure the steel blocks (through holespresent in each of the test blocks) to the upper and lower arms of thestud pull machine. The tensile pull speed used was 3.00 inches perminute, and the adhesion measurement was recorded in terms of pounds offorce. The tensile test results for the initial and post pressure cookerparts are presented in Table 1.

TABLE 1 Initial Adhesion (lbs) Retained Adhesion (lbs) 191 141 169 147179 112 180 153 166 126 155 138 174 161 175 121 111 133 149 149 164 154144 119

As the results in Table 1 demonstrate, the product was found to havegood initial and retained adhesion. The average adhesion for the partsprior to pressure cooker treatment was 163 pounds and after pressurecooker it was 138 pounds. Thus, even after one full week at twoatmospheres pressure of steam (14.7 psig, 121° C.) about 85% of theinitial adhesion was retained. It is noteworthy that a competitivematerial which was run at the same time had an initial adhesion of 338pounds, but dropped down to zero after the pressure cooker treatment.

EXAMPLE 10A

A composition was formulated using a monovinyl ether diluent and adivinyl ether “rubber” comonomer. The addition of these materials wasused to enhance certain properties of the adhesive composition.Specifically, the monovinyl ether was used to reduce the viscosity andincrease the thixotropic index (defined as the quotient of the 1 rpmover the 20 rpm viscosity). The “rubber” comonomer was used to“flexibilize” the cured adhesive. Flexibility is especially importantwhen thin bondlines are used since stress increases as bondlinedecreases. A convenient measure of stress for a cured part is the radiusof curvature (ROC). This measurement is traditionally done with asurface profilometer and is an index of the “bowing” of the silicon die.The higher the ROC (i.e., the larger the sphere described by measuredarc) the lower the stress. It is generally desirable to have an ROC≧onemeter. The composition described in Example 10 results in a radius ofcurvature of greater than 1.5 meters when used at a 2.0 mil bondline,but gives a ROC of less than one meter when the bondline is reduced to1.0 mils.

The monovinyl ether diluent used, vinyl octadecyl ether, was purchasedfrom BASF Corp. (Parsippany, N.J.). The divinyl ether “rubber” was theproduct described in Example 9B. An organic adhesive vehicle wasprepared using 1.29 grams (3.7 meqs) of the BMI prepared according toExample 8, 0.1125 grams (0.38 meqs) vinyl octadecyl ether, and 0.1127grams (0.08 meqs) of the divinyl ether prepared according to Example 9B.An additional 1.0% by weight dicumyl peroxide (initiator) and 2.7%gamma-methacryloxy-propyltrimethoxysilane coupling agent were added tocomplete the organic adhesive mix.

Twenty-seven percent by weight of the above organic adhesive mixture wasadded to 73% by weight of silver filler. The mixture was homogenizedunder high shear and then degassed using a full mechanical pump vacuum.The adhesive was dispensed into silver plated copper lead frames using astarfish dispense nozzle. Bare silicon dice (300×300 mil on a side) wereplaced on top and compressed into the adhesive to achieve a 1.0 milbondline. A similar set of parts was generated using the adhesivecomposition described in Example 10. The parts were cured for one minuteat 200° C. The radius of curvature for parts using the adhesivedescribed here was 1.29 meters. The ROC for the control parts was 0.76meters. The 10 rpm viscosity (Brookfield viscometer) for the adhesivedescribed here was 5,734 centipoise at 25.0° C. and the thixotropicindex was 6.60. The control adhesive had a 12,040 10 rpm viscosity at25.0° C. and a thixotropic index of 4.97. The post cure adhesion resultsfor the adhesive described here and the control were as follows:

TABLE 2 Adhesion for Test Paste Adhesion for Control (lbs) (lbs) 157 72149 139 154 175 134 149 158 97 159 136

The results presented here demonstrate that several of the adhesivecomposition properties can be improved with little or no sacrifice ofinitial adhesion by the incorporation of modest amounts of a reactivediluent and a flexibilizing comonomer.

EXAMPLE 10B

The previous examples demonstrated how adhesive compositions could beformulated in which no more than one equivalent of vinyl ether comonomeris used in conjunction with an excess of a bismaleimide. It is notnecessary to have any vinyl ether present in the composition, however.That is to say, that compositions may be formulated where maleimide isthe only polymerizable function.

Thus, an organic adhesive vehicle was prepared using 96.25% by weight ofthe BMI prepared according to Example 8, 1% by weight USP90MD[1,1bis(t-amyl peroxy) cyclohexane—an initiator available from WitcoCorporation, Marshall, Tex.], 0.76%gamma-methacryloxypropyl-trimethoxysilane (coupling agent), and 1.72%beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (coupling agent).

Twenty-five percent by weight of the above organic adhesive mixture wasadded to 75% by weight of silver metal filler. The mixture was shearedand degassed as before. Dispense and die placement were performed asdescribed earlier (300×300 mil silicon die on Ag coated Cu lead frames).The bondline used was 1.0 mils and the cure time was one minute at 200°C. Initial and post pressure cooker (16 hour) adhesion values arepresented in the following table.

TABLE 3 Initial Adhesion Post Pressure Cooker Adhesion (lbs) (lbs) 16583 137 188 115 143 171 122 148 208 154 200

This composition exhibited a narrow exotherm with a maxima at 128.8° C.via differential scanning calorimetry (DSC) and a weight loss of lessthan 0.75% by 350° C. according to TGA (10° C./min. using an air purge).This composition therefore demonstrates the viability of an “allmaleimidel” snap cure adhesive system.

EXAMPLE 10C

The previous examples have demonstrated the utility of maleimide/vinylether co-cure and maleimide homocure for use as adhesives. Otherpolymerizable functional groups including acrylate and methacrylate mayalso be used alone or in combination with maleimide and/or vinyl ethermonomers.

Thus, an organic adhesive vehicle was prepared using 4.00 grams of thediacrylate prepared according to Example 3B, 1.00 gram decanendioldimethacrylate (purchased from Polysciences, Inc., Warrington, Pa.), and1.00 gram Ricon R-130 Epoxy (obtained from Advanced Resins, Inc., GrandJunction, Colo.). Two percent by weight of dicumyl peroxide initiatorwas dissolved in this mix.

Twenty percent by weight of the organic adhesive mixture was added to80% by weight silver metal filler. The mixture was homogenized usinghigh shear and then degassed. Parts were assembled as before using300×300 silicon on Ag plated Cu lead frames. The cure condition was 200°C. for one minute, and the bondline thickness used was 1.0 mil. Theinitial adhesion values an the corresponding failure mode information ispresented in the following table:

TABLE 4 Initial Adhesion (lbs) Failure Mode (lbs) 66 material 55material 67 material 62 material 63 material 59 material

The measured adhesion for this mixture was lower than observed for mostof the BMI containing compositions. The failure mode, however, was ofthe most preferred (all material) type (i.e., entirely cohesive ratherthan adhesive failure). The radius of curvature for the cured adhesiveat the bondline thickness used here was 2.51 meters.

EXAMPLE 11

A test paste was made that contained one equivalent each of thebismaleimide of Versalink 650(polytetramethyleneoxide-di-p-aminobenzoate, marketed by Air Products,Allentown, Pa.) and the divinyl ether of tetraethylene glycol. Theorganic phase had 1% by weight of dicumyl peroxide. Seventy-five percentby weight silver filler was used in the paste. Ten parts were assembledand cured as per the preceding example using this paste that containedno coupling agent. One percent by weight of the same mixed couplingagents noted above were then added to the paste. Another ten parts wereassembled and cured using this new paste mix. Both groups of parts werethen divided into two sets. Half of the parts from each group was testedfor tensile strength immediately and the other half following four hoursof immersion in the pressure cooker. Tensile strength measurements wereperformed according to the procedure described in Example 10. Theresults of this testing are summarized in Table 5.

TABLE 5 Tensile Strength of Adhesive Bond No Coupling With CouplingAgent Agent Initial Value Post Moisture Initial Value Post Moisture110.7 0 112.3 88.8 111.2 0 102.6 84.3 107.7 0 108.5 83.8 110.5 0 109.287.9 106.5 0 115.6 93.3

The data in Table 5 shows that the presence of the coupling agents has adramatic impact on the survival of the adhesive bond in extreme moistureenvironments.

EXAMPLE 12

A test was conducted to test the adhesion performance of inventioncompositions following a one minute cure at 200° C. The bondline usedfor these parts was also dropped from 2.0 down to 1.0 mils during theattach step. Stress, which is induced by the large thermal mismatchbetween the silicon and lead frame, increases when the bondline isdecreased. The organic adhesive portion of paste consisted of oneequivalent each of the BMI prepared according to Example 8, and Vectomer4010 (i.e., bis(4-vinyloxybutyl)isophthalate). It also contained 4.5% ofgamma-methacryloxypropyl-trimethoxysilane coupling agent, as well as0.95% dicumyl peroxide initiator. A paste was made consisting of 22% byweight of this adhesive composition and 78% by weight of silver flake.The paste was degassed and then used to attach 300×300 mil silicon dieto silver plated copper lead frames using the reduced bondline and curetime. Six parts were assembled and cured. Two void test parts (sameconditions but using 300×300 mil glass slides to replace the silicondie) were also made. There was no evidence of porosity in the void testparts. Tensile strength measurements were performed according to theprocedure described in Example 10. The tensile test values for the otherparts were: 116, 114, 119, 122, 128 and 134 pounds force.

While the invention has been described in detail with reference tocertain preferred embodiments thereof, it will be understood thatmodifications and variations are within the spirit and scope of thatwhich is described and claimed.

1. A maleimide composition comprising (a) a liquid maleimide; and (b) aperoxide cure initiator, wherein said maleimide composition, whendispensed between a 300×300 mil silica die and a Ag coated lead frame asa 1 mil bondline and cured for 1 minute at a temperature of about 200°C., demonstrates an initial adhesion value of at least 115 lbs.
 2. Thecomposition of claim 1, substantially free of inert diluent.
 3. Acomposition comprising (a) a liquid maleimide comprising:

wherein: each R is independently hydrogen or lower alkyl, —X— is abranched chain alkyl or alkylene species having at least 12 carbonatoms, and m is 1, 2 or 3; (b) a peroxide cure initiator.
 4. An assemblycomprising a first article permanently adhered to a second article by acured aliquot of the composition of claim
 1. 5. An assembly comprising afirst article permanently adhered to a second article by a cured aliquotof the composition of claim
 3. 6. The composition of claim 1, furthercomprising a filler.
 7. The composition of claim 3, further comprising afiller.
 8. The composition of claim 3, substantially free of inertdiluent.
 9. The composition of claim 4, wherein the first article is asilicon die.
 10. The composition of claim 5, wherein the first articleis a silicon die.
 11. The maleimide composition according to eitherclaim 1 or 2, which exhibits a post pressure cooker adhesion of at least83 lbs.